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May 2009
It has been a while since I posted a copy of PEP 1 to the mailing
lists and newsgroups. I've recently done some updating of a few
sections, so in the interest of gaining wider community participation
in the Python development process, I'm posting the latest revision of
PEP 1 here. A version of the PEP is always available on-line at
http://www.python.org/peps/pep-0001.html
Enjoy,
-Barry
-------------------- snip snip --------------------
PEP: 1
Title: PEP Purpose and Guidelines
Version: $Revision: 1.36 $
Last-Modified: $Date: 2002/07/29 18:34:59 $
Author: Barry A. Warsaw, Jeremy Hylton
Status: Active
Type: Informational
Created: 13-Jun-2000
Post-History: 21-Mar-2001, 29-Jul-2002
What is a PEP?
PEP stands for Python Enhancement Proposal. A PEP is a design
document providing information to the Python community, or
describing a new feature for Python. The PEP should provide a
concise technical specification of the feature and a rationale for
the feature.
We intend PEPs to be the primary mechanisms for proposing new
features, for collecting community input on an issue, and for
documenting the design decisions that have gone into Python. The
PEP author is responsible for building consensus within the
community and documenting dissenting opinions.
Because the PEPs are maintained as plain text files under CVS
control, their revision history is the historical record of the
feature proposal[1].
Kinds of PEPs
There are two kinds of PEPs. A standards track PEP describes a
new feature or implementation for Python. An informational PEP
describes a Python design issue, or provides general guidelines or
information to the Python community, but does not propose a new
feature. Informational PEPs do not necessarily represent a Python
community consensus or recommendation, so users and implementors
are free to ignore informational PEPs or follow their advice.
PEP Work Flow
The PEP editor, Barry Warsaw <peps(a)python.org>, assigns numbers
for each PEP and changes its status.
The PEP process begins with a new idea for Python. It is highly
recommended that a single PEP contain a single key proposal or new
idea. The more focussed the PEP, the more successfully it tends
to be. The PEP editor reserves the right to reject PEP proposals
if they appear too unfocussed or too broad. If in doubt, split
your PEP into several well-focussed ones.
Each PEP must have a champion -- someone who writes the PEP using
the style and format described below, shepherds the discussions in
the appropriate forums, and attempts to build community consensus
around the idea. The PEP champion (a.k.a. Author) should first
attempt to ascertain whether the idea is PEP-able. Small
enhancements or patches often don't need a PEP and can be injected
into the Python development work flow with a patch submission to
the SourceForge patch manager[2] or feature request tracker[3].
The PEP champion then emails the PEP editor <peps(a)python.org> with
a proposed title and a rough, but fleshed out, draft of the PEP.
This draft must be written in PEP style as described below.
If the PEP editor approves, he will assign the PEP a number, label
it as standards track or informational, give it status 'draft',
and create and check-in the initial draft of the PEP. The PEP
editor will not unreasonably deny a PEP. Reasons for denying PEP
status include duplication of effort, being technically unsound,
not providing proper motivation or addressing backwards
compatibility, or not in keeping with the Python philosophy. The
BDFL (Benevolent Dictator for Life, Guido van Rossum) can be
consulted during the approval phase, and is the final arbitrator
of the draft's PEP-ability.
If a pre-PEP is rejected, the author may elect to take the pre-PEP
to the comp.lang.python newsgroup (a.k.a. python-list(a)python.org
mailing list) to help flesh it out, gain feedback and consensus
from the community at large, and improve the PEP for
re-submission.
The author of the PEP is then responsible for posting the PEP to
the community forums, and marshaling community support for it. As
updates are necessary, the PEP author can check in new versions if
they have CVS commit permissions, or can email new PEP versions to
the PEP editor for committing.
Standards track PEPs consists of two parts, a design document and
a reference implementation. The PEP should be reviewed and
accepted before a reference implementation is begun, unless a
reference implementation will aid people in studying the PEP.
Standards Track PEPs must include an implementation - in the form
of code, patch, or URL to same - before it can be considered
Final.
PEP authors are responsible for collecting community feedback on a
PEP before submitting it for review. A PEP that has not been
discussed on python-list(a)python.org and/or python-dev(a)python.org
will not be accepted. However, wherever possible, long open-ended
discussions on public mailing lists should be avoided. Strategies
to keep the discussions efficient include, setting up a separate
SIG mailing list for the topic, having the PEP author accept
private comments in the early design phases, etc. PEP authors
should use their discretion here.
Once the authors have completed a PEP, they must inform the PEP
editor that it is ready for review. PEPs are reviewed by the BDFL
and his chosen consultants, who may accept or reject a PEP or send
it back to the author(s) for revision.
Once a PEP has been accepted, the reference implementation must be
completed. When the reference implementation is complete and
accepted by the BDFL, the status will be changed to `Final.'
A PEP can also be assigned status `Deferred.' The PEP author or
editor can assign the PEP this status when no progress is being
made on the PEP. Once a PEP is deferred, the PEP editor can
re-assign it to draft status.
A PEP can also be `Rejected'. Perhaps after all is said and done
it was not a good idea. It is still important to have a record of
this fact.
PEPs can also be replaced by a different PEP, rendering the
original obsolete. This is intended for Informational PEPs, where
version 2 of an API can replace version 1.
PEP work flow is as follows:
Draft -> Accepted -> Final -> Replaced
^
+----> Rejected
v
Deferred
Some informational PEPs may also have a status of `Active' if they
are never meant to be completed. E.g. PEP 1.
What belongs in a successful PEP?
Each PEP should have the following parts:
1. Preamble -- RFC822 style headers containing meta-data about the
PEP, including the PEP number, a short descriptive title
(limited to a maximum of 44 characters), the names, and
optionally the contact info for each author, etc.
2. Abstract -- a short (~200 word) description of the technical
issue being addressed.
3. Copyright/public domain -- Each PEP must either be explicitly
labelled as placed in the public domain (see this PEP as an
example) or licensed under the Open Publication License[4].
4. Specification -- The technical specification should describe
the syntax and semantics of any new language feature. The
specification should be detailed enough to allow competing,
interoperable implementations for any of the current Python
platforms (CPython, JPython, Python .NET).
5. Motivation -- The motivation is critical for PEPs that want to
change the Python language. It should clearly explain why the
existing language specification is inadequate to address the
problem that the PEP solves. PEP submissions without
sufficient motivation may be rejected outright.
6. Rationale -- The rationale fleshes out the specification by
describing what motivated the design and why particular design
decisions were made. It should describe alternate designs that
were considered and related work, e.g. how the feature is
supported in other languages.
The rationale should provide evidence of consensus within the
community and discuss important objections or concerns raised
during discussion.
7. Backwards Compatibility -- All PEPs that introduce backwards
incompatibilities must include a section describing these
incompatibilities and their severity. The PEP must explain how
the author proposes to deal with these incompatibilities. PEP
submissions without a sufficient backwards compatibility
treatise may be rejected outright.
8. Reference Implementation -- The reference implementation must
be completed before any PEP is given status 'Final,' but it
need not be completed before the PEP is accepted. It is better
to finish the specification and rationale first and reach
consensus on it before writing code.
The final implementation must include test code and
documentation appropriate for either the Python language
reference or the standard library reference.
PEP Template
PEPs are written in plain ASCII text, and should adhere to a
rigid style. There is a Python script that parses this style and
converts the plain text PEP to HTML for viewing on the web[5].
PEP 9 contains a boilerplate[7] template you can use to get
started writing your PEP.
Each PEP must begin with an RFC822 style header preamble. The
headers must appear in the following order. Headers marked with
`*' are optional and are described below. All other headers are
required.
PEP: <pep number>
Title: <pep title>
Version: <cvs version string>
Last-Modified: <cvs date string>
Author: <list of authors' real names and optionally, email addrs>
* Discussions-To: <email address>
Status: <Draft | Active | Accepted | Deferred | Final | Replaced>
Type: <Informational | Standards Track>
* Requires: <pep numbers>
Created: <date created on, in dd-mmm-yyyy format>
* Python-Version: <version number>
Post-History: <dates of postings to python-list and python-dev>
* Replaces: <pep number>
* Replaced-By: <pep number>
The Author: header lists the names and optionally, the email
addresses of all the authors/owners of the PEP. The format of the
author entry should be
address(a)dom.ain (Random J. User)
if the email address is included, and just
Random J. User
if the address is not given. If there are multiple authors, each
should be on a separate line following RFC 822 continuation line
conventions. Note that personal email addresses in PEPs will be
obscured as a defense against spam harvesters.
Standards track PEPs must have a Python-Version: header which
indicates the version of Python that the feature will be released
with. Informational PEPs do not need a Python-Version: header.
While a PEP is in private discussions (usually during the initial
Draft phase), a Discussions-To: header will indicate the mailing
list or URL where the PEP is being discussed. No Discussions-To:
header is necessary if the PEP is being discussed privately with
the author, or on the python-list or python-dev email mailing
lists. Note that email addresses in the Discussions-To: header
will not be obscured.
Created: records the date that the PEP was assigned a number,
while Post-History: is used to record the dates of when new
versions of the PEP are posted to python-list and/or python-dev.
Both headers should be in dd-mmm-yyyy format, e.g. 14-Aug-2001.
PEPs may have a Requires: header, indicating the PEP numbers that
this PEP depends on.
PEPs may also have a Replaced-By: header indicating that a PEP has
been rendered obsolete by a later document; the value is the
number of the PEP that replaces the current document. The newer
PEP must have a Replaces: header containing the number of the PEP
that it rendered obsolete.
PEP Formatting Requirements
PEP headings must begin in column zero and the initial letter of
each word must be capitalized as in book titles. Acronyms should
be in all capitals. The body of each section must be indented 4
spaces. Code samples inside body sections should be indented a
further 4 spaces, and other indentation can be used as required to
make the text readable. You must use two blank lines between the
last line of a section's body and the next section heading.
You must adhere to the Emacs convention of adding two spaces at
the end of every sentence. You should fill your paragraphs to
column 70, but under no circumstances should your lines extend
past column 79. If your code samples spill over column 79, you
should rewrite them.
Tab characters must never appear in the document at all. A PEP
should include the standard Emacs stanza included by example at
the bottom of this PEP.
A PEP must contain a Copyright section, and it is strongly
recommended to put the PEP in the public domain.
When referencing an external web page in the body of a PEP, you
should include the title of the page in the text, with a
footnote reference to the URL. Do not include the URL in the body
text of the PEP. E.g.
Refer to the Python Language web site [1] for more details.
...
[1] http://www.python.org
When referring to another PEP, include the PEP number in the body
text, such as "PEP 1". The title may optionally appear. Add a
footnote reference that includes the PEP's title and author. It
may optionally include the explicit URL on a separate line, but
only in the References section. Note that the pep2html.py script
will calculate URLs automatically, e.g.:
...
Refer to PEP 1 [7] for more information about PEP style
...
References
[7] PEP 1, PEP Purpose and Guidelines, Warsaw, Hylton
http://www.python.org/peps/pep-0001.html
If you decide to provide an explicit URL for a PEP, please use
this as the URL template:
http://www.python.org/peps/pep-xxxx.html
PEP numbers in URLs must be padded with zeros from the left, so as
to be exactly 4 characters wide, however PEP numbers in text are
never padded.
Reporting PEP Bugs, or Submitting PEP Updates
How you report a bug, or submit a PEP update depends on several
factors, such as the maturity of the PEP, the preferences of the
PEP author, and the nature of your comments. For the early draft
stages of the PEP, it's probably best to send your comments and
changes directly to the PEP author. For more mature, or finished
PEPs you may want to submit corrections to the SourceForge bug
manager[6] or better yet, the SourceForge patch manager[2] so that
your changes don't get lost. If the PEP author is a SF developer,
assign the bug/patch to him, otherwise assign it to the PEP
editor.
When in doubt about where to send your changes, please check first
with the PEP author and/or PEP editor.
PEP authors who are also SF committers, can update the PEPs
themselves by using "cvs commit" to commit their changes.
Remember to also push the formatted PEP text out to the web by
doing the following:
% python pep2html.py -i NUM
where NUM is the number of the PEP you want to push out. See
% python pep2html.py --help
for details.
Transferring PEP Ownership
It occasionally becomes necessary to transfer ownership of PEPs to
a new champion. In general, we'd like to retain the original
author as a co-author of the transferred PEP, but that's really up
to the original author. A good reason to transfer ownership is
because the original author no longer has the time or interest in
updating it or following through with the PEP process, or has
fallen off the face of the 'net (i.e. is unreachable or not
responding to email). A bad reason to transfer ownership is
because you don't agree with the direction of the PEP. We try to
build consensus around a PEP, but if that's not possible, you can
always submit a competing PEP.
If you are interested assuming ownership of a PEP, send a message
asking to take over, addressed to both the original author and the
PEP editor <peps(a)python.org>. If the original author doesn't
respond to email in a timely manner, the PEP editor will make a
unilateral decision (it's not like such decisions can be
reversed. :).
References and Footnotes
[1] This historical record is available by the normal CVS commands
for retrieving older revisions. For those without direct access
to the CVS tree, you can browse the current and past PEP revisions
via the SourceForge web site at
http://cvs.sourceforge.net/cgi-bin/cvsweb.cgi/python/nondist/peps/?cvsroot=…
[2] http://sourceforge.net/tracker/?group_id=5470&atid=305470
[3] http://sourceforge.net/tracker/?atid=355470&group_id=5470&func=browse
[4] http://www.opencontent.org/openpub/
[5] The script referred to here is pep2html.py, which lives in
the same directory in the CVS tree as the PEPs themselves.
Try "pep2html.py --help" for details.
The URL for viewing PEPs on the web is
http://www.python.org/peps/
[6] http://sourceforge.net/tracker/?group_id=5470&atid=305470
[7] PEP 9, Sample PEP Template
http://www.python.org/peps/pep-0009.html
Copyright
This document has been placed in the public domain.
Local Variables:
mode: indented-text
indent-tabs-mode: nil
sentence-end-double-space: t
fill-column: 70
End:
I've received some enthusiastic emails from someone who wants to
revive restricted mode. He started out with a bunch of patches to the
CPython runtime using ctypes, which he attached to an App Engine bug:
http://code.google.com/p/googleappengine/issues/detail?id=671
Based on his code (the file secure.py is all you need, included in
secure.tar.gz) it seems he believes the only security leaks are
__subclasses__, gi_frame and gi_code. (I have since convinced him that
if we add "restricted" guards to these attributes, he doesn't need the
functions added to sys.)
I don't recall the exploits that Samuele once posted that caused the
death of rexec.py -- does anyone recall, or have a pointer to the
threads?
--
--Guido van Rossum (home page: http://www.python.org/~guido/)
I propose the following PEP for inclusion to Python 3.1.
Please comment.
Regards,
Martin
Abstract
========
Namespace packages are a mechanism for splitting a single Python
package across multiple directories on disk. In current Python
versions, an algorithm to compute the packages __path__ must be
formulated. With the enhancement proposed here, the import machinery
itself will construct the list of directories that make up the
package.
Terminology
===========
Within this PEP, the term package refers to Python packages as defined
by Python's import statement. The term distribution refers to
separately installable sets of Python modules as stored in the Python
package index, and installed by distutils or setuptools. The term
vendor package refers to groups of files installed by an operating
system's packaging mechanism (e.g. Debian or Redhat packages install
on Linux systems).
The term portion refers to a set of files in a single directory (possibly
stored in a zip file) that contribute to a namespace package.
Namespace packages today
========================
Python currently provides the pkgutil.extend_path to denote a package as
a namespace package. The recommended way of using it is to put::
from pkgutil import extend_path
__path__ = extend_path(__path__, __name__)
int the package's ``__init__.py``. Every distribution needs to provide
the same contents in its ``__init__.py``, so that extend_path is
invoked independent of which portion of the package gets imported
first. As a consequence, the package's ``__init__.py`` cannot
practically define any names as it depends on the order of the package
fragments on sys.path which portion is imported first. As a special
feature, extend_path reads files named ``*.pkg`` which allow to
declare additional portions.
setuptools provides a similar function pkg_resources.declare_namespace
that is used in the form::
import pkg_resources
pkg_resources.declare_namespace(__name__)
In the portion's __init__.py, no assignment to __path__ is necessary,
as declare_namespace modifies the package __path__ through sys.modules.
As a special feature, declare_namespace also supports zip files, and
registers the package name internally so that future additions to sys.path
by setuptools can properly add additional portions to each package.
setuptools allows declaring namespace packages in a distribution's
setup.py, so that distribution developers don't need to put the
magic __path__ modification into __init__.py themselves.
Rationale
=========
The current imperative approach to namespace packages has lead to
multiple slightly-incompatible mechanisms for providing namespace
packages. For example, pkgutil supports ``*.pkg`` files; setuptools
doesn't. Likewise, setuptools supports inspecting zip files, and
supports adding portions to its _namespace_packages variable, whereas
pkgutil doesn't.
In addition, the current approach causes problems for system vendors.
Vendor packages typically must not provide overlapping files, and an
attempt to install a vendor package that has a file already on disk
will fail or cause unpredictable behavior. As vendors might chose to
package distributions such that they will end up all in a single
directory for the namespace package, all portions would contribute
conflicting __init__.py files.
Specification
=============
Rather than using an imperative mechanism for importing packages, a
declarative approach is proposed here, as an extension to the existing
``*.pkg`` mechanism.
The import statement is extended so that it directly considers ``*.pkg``
files during import; a directory is considered a package if it either
contains a file named __init__.py, or a file whose name ends with
".pkg".
In addition, the format of the ``*.pkg`` file is extended: a line with
the single character ``*`` indicates that the entire sys.path will
be searched for portions of the namespace package at the time the
namespace packages is imported.
Importing a package will immediately compute the package's __path__;
the ``*.pkg`` files are not considered anymore after the initial import.
If a ``*.pkg`` package contains an asterisk, this asterisk is prepended
to the package's __path__ to indicate that the package is a namespace
package (and that thus further extensions to sys.path might also
want to extend __path__). At most one such asterisk gets prepended
to the path.
extend_path will be extended to recognize namespace packages according
to this PEP, and avoid adding directories twice to __path__.
No other change to the importing mechanism is made; searching
modules (including __init__.py) will continue to stop at the first
module encountered.
Discussion
==========
With the addition of ``*.pkg`` files to the import mechanism, namespace
packages can stop filling out the namespace package's __init__.py.
As a consequence, extend_path and declare_namespace become obsolete.
It is recommended that distributions put a file <distribution>.pkg
into their namespace packages, with a single asterisk. This allows
vendor packages to install multiple portions of namespace package
into a single directory, with no risk of overlapping files.
Namespace packages can start providing non-trivial __init__.py
implementations; to do so, it is recommended that a single distribution
provides a portion with just the namespace package's __init__.py
(and potentially other modules that belong to the namespace package
proper).
The mechanism is mostly compatible with the existing namespace
mechanisms. extend_path will be adjusted to this specification;
any other mechanism might cause portions to get added twice to
__path__.
Copyright
=========
This document has been placed in the public domain.
Hello everyone!
We have been encountering several deadlocks in a threaded Python
application which calls subprocess.Popen (i.e. fork()) in some of its
threads.
This has occurred on Python 2.4.1 on a 2.4.27 Linux kernel.
Preliminary analysis of the hang shows that the child process blocks
upon entering the execvp function, in which the import_lock is acquired
due to the following line:
def _ execvpe(file, args, env=None):
from errno import ENOENT, ENOTDIR
...
It is known that when forking from a pthreaded application, acquisition
attempts on locks which were already locked by other threads while
fork() was called will deadlock.
Due to these oddities we were wondering if it would be better to extract
the above import line from the execvpe call, to prevent lock
acquisition attempts in such cases.
Another workaround could be re-assigning a new lock to import_lock
(such a thing is done with the global interpreter lock) at PyOS_AfterFork or
pthread_atfork.
We'd appreciate any opinions you might have on the subject.
Thanks in advance,
Yair and Rotem
hey, has anyone investigated compiling python2.5 using winegcc, under wine?
i'm presently working my way through it, just for kicks, and was
wondering if anyone would like to pitch in or stare at the mess under
a microscope.
it's not as crazed as it sounds. cross-compiling python2.5 for win32
with mingw32 is an absolute miserable bitch of a job that goes
horribly wrong when you actually try to use the minimalist compiler to
do any real work.
so i figured that it would be easier to get python compiled using
wine. i _have_ got some success - a python script and a python.exe.so
(which is winegcc's friendly way of telling you you have something
that stands a chance of working) as well as a libpython25.dll.so.
what i _don't_ yet have is an _md5.dll (or should it be _md5.lib?)
i.e. the standard modules are a bit... iffy. the _winreg.o is
compiled; the _md5.o is compiled; the winreg.lib is not. whoops.
plus, it's necessary to enable nt_dl.c which is in PC/ _not_ in
Modules/.
one of the key issues that's a bit of a bitch is that python is
compiled up for win32 with a hard-coded pyconfig.h which someone went
to a _lot_ of trouble to create by hand instead of using autoconf. oh
- and it uses visualstudio so there's not even a Makefile. ignoring
that for the time-being was what allowed me to get as far as actually
having a python interpreter (with no c-based modules).
so there's a whole _stack_ of stuff that needs dragging kicking and
screaming into the 21st century.
there _is_ a reason why i want to do this. actually, there's two.
firstly, i sure as shit do _not_ want to buy, download, install _or_
run visual studio. i flat-out refuse to run an MS os and visual
studio runs like a dog under wine.
secondly, i want a python25.lib which i can use to cross-compile
modules for poor windows users _despite_ sticking to my principles and
keeping my integrity as a free software developer.
thirdly i'd like to cross-compile pywebkitgtk for win32
fourthly i'd like to compile and link applications to the extremely
successful and well wicked MSHTML.DLL... in the _wine_ project :) not
the one in windows (!) i want to experiment with DOM model
manipulation - from python - similar to the OLPC HulaHop project -
_but_ i want to compile or cross-compile everything from linux, not
windows (see 1 above)
fifthly i'd like to see COM (DCOM) working and pywin32 compiled and
useable under wine, even if it means having to get a license to use
dcom98 and oleauth.lib and oleauth.h etc. and all the developer files
needed to link DCOM applications under windows. actually what i'd
_really_ like to see is FreeDCE's DCOM work actually damn well
finished, it's only been eight years since wez committed the first
versions of the IDL and header files, and it's only been over fifteen
years since microsoft began its world domination using COM and DCOM.
... but that's another story :)
so that's ... five reasons not two. if anyone would like to
collaborate on a crazed project with someone who can't count, i'm
happy to make available what i've got up to so far, on github.org.
l.
Hi,
I'd like to bring up the general idea of using a PSF slot in GSoC2009
to improve the Python development infrastructure. I also happen to
have two concrete proposals for that (such a coincidence!). But I
assure you the general idea is more important than my proposals :)
General:
Solving issues that get in core devs' way when they work on Python
development could be a nice PSF GSoC project.
I believe there are enough code related tasks that would greatly
improve Python development workflow but lack manpower to complete.
E.g., ISTM that a student working on svnmerge in past SoC editions
would've been able to mitigate some painful shortcomings. If the core
developers could come up with a list of peeves that would be solvable
in code (in existing tools), that would allow for a very useful GSoC
proposal.
Proposals:
These might fit the description above, and they're both tracker
related (yep, one-trick-pony here). The upside is that at least one
potential mentor is available for each, and I'd be able to offer
support to the student.
First, the PSF could invest a slot on integrating different tools of
the development workflow. Variations of 'file issue at bug tracker,
submit code for review' or 'branch locally to virtualenv, upload
failing testcase to tracker, upload patch to tracker' command line
utils. If these could be developed as general tools (i.e., not deeply
tied to Python dev infrastructure), Ali Afshar from PIDA is willing to
mentor it. I'd be available to help with Roundup and Rietveld
(integration in progress), but would like to see it work with
Launchpad, Bugzilla, Google Code and Review Board :)
The other proposal is to use a slot in Roundup proper and the Python
tracker instance. This could have a core Roundup developer as mentor,
under the condition it's focused on Roundup itself. IMO, are some
missing/broken core features in Roundup that would have a positive
impact on our tracker, mostly those relating to searches, security and
UI. I'd have a lot to contribute to the Python tracker part, based on
ongoing work.
Even if neither is considered worthy, I'll keep them on my to-do list
and hope to slowly and hackishly work towards both proposals' goals.
Barring feedback saying that they're out of scope, stupid and
downright offensive, I'll post details on each to this thread very
soon.
So, if the PSF was to use a slot on improving the way you work on
Python development, what would you like to see fixed or implemented?
Best regards,
Daniel
On Wed, 10 Nov 2004, John P Speno wrote:
Hi, sorry for the delayed response.
> While using subprocess (aka popen5), I came across one potential gotcha. I've had
> exceptions ending like this:
>
> File "test.py", line 5, in test
> cmd = popen5.Popen(args, stdout=PIPE)
> File "popen5.py", line 577, in __init__
> data = os.read(errpipe_read, 1048576) # Exceptions limited to 1 MB
> OSError: [Errno 4] Interrupted system call
>
> (on Solaris 9)
>
> Would it make sense for subprocess to use a more robust read() function
> which can handle these cases, i.e. when the parent's read on the pipe
> to the child's stderr is interrupted by a system call, and returns EINTR?
> I imagine it could catch EINTR and EAGAIN and retry the failed read().
I assume you are using signals in your application? The os.read above is
not the only system call that can fail with EINTR. subprocess.py is full
of other system calls that can fail, and I suspect that many other Python
modules are as well.
I've made a patch (attached) to subprocess.py (and test_subprocess.py)
that should guard against EINTR, but I haven't committed it yet. It's
quite large.
Are Python modules supposed to handle EINTR? Why not let the C code handle
this? Or, perhaps the signal module should provide a sigaction function,
so that users can use SA_RESTART.
Index: subprocess.py
===================================================================
RCS file: /cvsroot/python/python/dist/src/Lib/subprocess.py,v
retrieving revision 1.8
diff -u -r1.8 subprocess.py
--- subprocess.py 7 Nov 2004 14:30:34 -0000 1.8
+++ subprocess.py 17 Nov 2004 19:42:30 -0000
@@ -888,6 +888,50 @@
pass
+ def _read_no_intr(self, fd, buffersize):
+ """Like os.read, but retries on EINTR"""
+ while True:
+ try:
+ return os.read(fd, buffersize)
+ except OSError, e:
+ if e.errno == errno.EINTR:
+ continue
+ else:
+ raise
+
+
+ def _read_all(self, fd, buffersize):
+ """Like os.read, but retries on EINTR, and reads until EOF"""
+ all = ""
+ while True:
+ data = self._read_no_intr(fd, buffersize)
+ all += data
+ if data == "":
+ return all
+
+
+ def _write_no_intr(self, fd, s):
+ """Like os.write, but retries on EINTR"""
+ while True:
+ try:
+ return os.write(fd, s)
+ except OSError, e:
+ if e.errno == errno.EINTR:
+ continue
+ else:
+ raise
+
+ def _waitpid_no_intr(self, pid, options):
+ """Like os.waitpid, but retries on EINTR"""
+ while True:
+ try:
+ return os.waitpid(pid, options)
+ except OSError, e:
+ if e.errno == errno.EINTR:
+ continue
+ else:
+ raise
+
def _execute_child(self, args, executable, preexec_fn, close_fds,
cwd, env, universal_newlines,
startupinfo, creationflags, shell,
@@ -963,7 +1007,7 @@
exc_value,
tb)
exc_value.child_traceback = ''.join(exc_lines)
- os.write(errpipe_write, pickle.dumps(exc_value))
+ self._write_no_intr(errpipe_write, pickle.dumps(exc_value))
# This exitcode won't be reported to applications, so it
# really doesn't matter what we return.
@@ -979,7 +1023,7 @@
os.close(errwrite)
# Wait for exec to fail or succeed; possibly raising exception
- data = os.read(errpipe_read, 1048576) # Exceptions limited to 1 MB
+ data = self._read_all(errpipe_read, 1048576) # Exceptions limited to 1 MB
os.close(errpipe_read)
if data != "":
child_exception = pickle.loads(data)
@@ -1003,7 +1047,7 @@
attribute."""
if self.returncode == None:
try:
- pid, sts = os.waitpid(self.pid, os.WNOHANG)
+ pid, sts = self._waitpid_no_intr(self.pid, os.WNOHANG)
if pid == self.pid:
self._handle_exitstatus(sts)
except os.error:
@@ -1015,7 +1059,7 @@
"""Wait for child process to terminate. Returns returncode
attribute."""
if self.returncode == None:
- pid, sts = os.waitpid(self.pid, 0)
+ pid, sts = self._waitpid_no_intr(self.pid, 0)
self._handle_exitstatus(sts)
return self.returncode
@@ -1049,27 +1093,33 @@
stderr = []
while read_set or write_set:
- rlist, wlist, xlist = select.select(read_set, write_set, [])
+ try:
+ rlist, wlist, xlist = select.select(read_set, write_set, [])
+ except select.error, e:
+ if e[0] == errno.EINTR:
+ continue
+ else:
+ raise
if self.stdin in wlist:
# When select has indicated that the file is writable,
# we can write up to PIPE_BUF bytes without risk
# blocking. POSIX defines PIPE_BUF >= 512
- bytes_written = os.write(self.stdin.fileno(), input[:512])
+ bytes_written = self._write_no_intr(self.stdin.fileno(), input[:512])
input = input[bytes_written:]
if not input:
self.stdin.close()
write_set.remove(self.stdin)
if self.stdout in rlist:
- data = os.read(self.stdout.fileno(), 1024)
+ data = self._read_no_intr(self.stdout.fileno(), 1024)
if data == "":
self.stdout.close()
read_set.remove(self.stdout)
stdout.append(data)
if self.stderr in rlist:
- data = os.read(self.stderr.fileno(), 1024)
+ data = self._read_no_intr(self.stderr.fileno(), 1024)
if data == "":
self.stderr.close()
read_set.remove(self.stderr)
Index: test/test_subprocess.py
===================================================================
RCS file: /cvsroot/python/python/dist/src/Lib/test/test_subprocess.py,v
retrieving revision 1.14
diff -u -r1.14 test_subprocess.py
--- test/test_subprocess.py 12 Nov 2004 15:51:48 -0000 1.14
+++ test/test_subprocess.py 17 Nov 2004 19:42:30 -0000
@@ -7,6 +7,7 @@
import tempfile
import time
import re
+import errno
mswindows = (sys.platform == "win32")
@@ -35,6 +36,16 @@
fname = tempfile.mktemp()
return os.open(fname, os.O_RDWR|os.O_CREAT), fname
+ def read_no_intr(self, obj):
+ while True:
+ try:
+ return obj.read()
+ except IOError, e:
+ if e.errno == errno.EINTR:
+ continue
+ else:
+ raise
+
#
# Generic tests
#
@@ -123,7 +134,7 @@
p = subprocess.Popen([sys.executable, "-c",
'import sys; sys.stdout.write("orange")'],
stdout=subprocess.PIPE)
- self.assertEqual(p.stdout.read(), "orange")
+ self.assertEqual(self.read_no_intr(p.stdout), "orange")
def test_stdout_filedes(self):
# stdout is set to open file descriptor
@@ -151,7 +162,7 @@
p = subprocess.Popen([sys.executable, "-c",
'import sys; sys.stderr.write("strawberry")'],
stderr=subprocess.PIPE)
- self.assertEqual(remove_stderr_debug_decorations(p.stderr.read()),
+ self.assertEqual(remove_stderr_debug_decorations(self.read_no_intr(p.stderr)),
"strawberry")
def test_stderr_filedes(self):
@@ -186,7 +197,7 @@
'sys.stderr.write("orange")'],
stdout=subprocess.PIPE,
stderr=subprocess.STDOUT)
- output = p.stdout.read()
+ output = self.read_no_intr(p.stdout)
stripped = remove_stderr_debug_decorations(output)
self.assertEqual(stripped, "appleorange")
@@ -220,7 +231,7 @@
stdout=subprocess.PIPE,
cwd=tmpdir)
normcase = os.path.normcase
- self.assertEqual(normcase(p.stdout.read()), normcase(tmpdir))
+ self.assertEqual(normcase(self.read_no_intr(p.stdout)), normcase(tmpdir))
def test_env(self):
newenv = os.environ.copy()
@@ -230,7 +241,7 @@
'sys.stdout.write(os.getenv("FRUIT"))'],
stdout=subprocess.PIPE,
env=newenv)
- self.assertEqual(p.stdout.read(), "orange")
+ self.assertEqual(self.read_no_intr(p.stdout), "orange")
def test_communicate(self):
p = subprocess.Popen([sys.executable, "-c",
@@ -305,7 +316,8 @@
'sys.stdout.write("\\nline6");'],
stdout=subprocess.PIPE,
universal_newlines=1)
- stdout = p.stdout.read()
+
+ stdout = self.read_no_intr(p.stdout)
if hasattr(open, 'newlines'):
# Interpreter with universal newline support
self.assertEqual(stdout,
@@ -343,7 +355,7 @@
def test_no_leaking(self):
# Make sure we leak no resources
- max_handles = 1026 # too much for most UNIX systems
+ max_handles = 10 # too much for most UNIX systems
if mswindows:
max_handles = 65 # a full test is too slow on Windows
for i in range(max_handles):
@@ -424,7 +436,7 @@
'sys.stdout.write(os.getenv("FRUIT"))'],
stdout=subprocess.PIPE,
preexec_fn=lambda: os.putenv("FRUIT", "apple"))
- self.assertEqual(p.stdout.read(), "apple")
+ self.assertEqual(self.read_no_intr(p.stdout), "apple")
def test_args_string(self):
# args is a string
@@ -457,7 +469,7 @@
p = subprocess.Popen(["echo $FRUIT"], shell=1,
stdout=subprocess.PIPE,
env=newenv)
- self.assertEqual(p.stdout.read().strip(), "apple")
+ self.assertEqual(self.read_no_intr(p.stdout).strip(), "apple")
def test_shell_string(self):
# Run command through the shell (string)
@@ -466,7 +478,7 @@
p = subprocess.Popen("echo $FRUIT", shell=1,
stdout=subprocess.PIPE,
env=newenv)
- self.assertEqual(p.stdout.read().strip(), "apple")
+ self.assertEqual(self.read_no_intr(p.stdout).strip(), "apple")
def test_call_string(self):
# call() function with string argument on UNIX
@@ -525,7 +537,7 @@
p = subprocess.Popen(["set"], shell=1,
stdout=subprocess.PIPE,
env=newenv)
- self.assertNotEqual(p.stdout.read().find("physalis"), -1)
+ self.assertNotEqual(self.read_no_intr(p.stdout).find("physalis"), -1)
def test_shell_string(self):
# Run command through the shell (string)
@@ -534,7 +546,7 @@
p = subprocess.Popen("set", shell=1,
stdout=subprocess.PIPE,
env=newenv)
- self.assertNotEqual(p.stdout.read().find("physalis"), -1)
+ self.assertNotEqual(self.read_no_intr(p.stdout).find("physalis"), -1)
def test_call_string(self):
# call() function with string argument on Windows
/Peter Åstrand <astrand(a)lysator.liu.se>
Consider the code:
code = "def Foo():\n\n pass\n\n "
This code is malformed in that the final indentation (2 spaces) does not agree with the previous indentation of the pass statement (4 spaces). Or maybe it's just fine if you take the blank lines should be ignored statement from the docs to be true. So let's look at different ways I can consume this code.
If I use compile to compile this:
compile(code, 'foo', 'single')
I get an IndentationError: unindent does not match any outer indentation level
But if I put this in a file:
f= file('indenttest.py', 'w')
f.write(code)
f.close()
import indenttest
It imports just fine.
If I run it through the tokenize module it also tokenizes just fine:
>>> import tokenize
>>> from cStringIO import StringIO
>>> tokenize.tokenize(StringIO(code).readline)
1,0-1,3: NAME 'def'
1,5-1,8: NAME 'Foo'
1,8-1,9: OP '('
1,9-1,10: OP ')'
1,10-1,11: OP ':'
1,11-1,12: NEWLINE '\n'
2,0-2,1: NL '\n'
3,0-3,4: INDENT ' '
3,4-3,8: NAME 'pass'
3,8-3,9: NEWLINE '\n'
4,0-4,1: NL '\n'
5,0-5,0: DEDENT ''
5,0-5,0: ENDMARKER ''
And if it fails anywhere it would seem tokenization is where it should fail - especially given that tokenize.py seems to report this error on other occasions.
And stranger still if I add a new line then it will even compile fine:
compile(code + '\n', 'foo', 'single')
Which seems strange because in either case all of the trailing lines are blank lines and as such should basically be ignored according to the documentation.
Is there some strange reason why compile rejects what everything else agrees is perfectly valid code?
On Wed, May 27, 2009 at 06:02:57PM -0600, Brian de Alwis wrote:
> With Python having recently chosen to switch to Mercurial, I hoped
> that any developers who've used a DVCS (and who are over 18 years
> old) might like to participate in our survey and share your
Just curious. Why is this age restriction? You might miss out few
key developers...
--
Senthil
Hi, guys,
just a short introduction of one of this year's GSoC PSF projects:
I am implementing a support for per-paragraph comments and user/developer
interface for submitting/committing fixes in Sphinx[1].
In case you are interesed in adding your 2 cents (or more) by commenting
on my application[2] or proposing some enhancements - feel free to do so
on sphinx-dev[3]. Or take a look at my blog to keep up to date[4].
[1] - http://sphinx.pocoo.org/
[2] - http://tosh.pl/gminick/gsoc/sphinx/
[3] - http://groups.google.com/group/sphinx-dev
[4] - http://gminick.wordpress.com
Best regards,
--
Wojtek Walczak
http://tosh.pl/gminick/
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